What follows here
is the modification that will allow the GM3SEK triode board to work with a
toroid type transformer that supplies the high volts for the anode, and, the
supply for the tube heaters. (this might also include lows volts for control,
such as 18vac for 12vDC relays)
information comes from Ian GM3SEK himself.
the "TRIODE BOARD" printing along the bottom edge of the board.
Immediately above the "R" in "BOARD" is a plated-through hole - this is
the warm-up control signal coming from U3 (LM555CN).
Using a sharp 3mm drill held in your fingertips, countersink this hole
from the top, just enough to remove the top copper and break the
connection. Check with an ohmmeter that there is no continuity.
One side of this broken connection goes to pin 11 of U5. Underneath the
board, link pin 11 to pin 14 (+12V). Double-check that you have
identified the correct pins!
Remove the HV_OK input pin and remove D6, C11, R11 and R12. That leaves
nothing connected to U5 pin 3. Instead, link pin 3 to the bottom side of
the connection that you drilled out in step 2. The warm-up timer will
now block the PTT, using what used to be the HV_OK input.
Re-check everything and re-insert the ICs. You should now find that
HV_CTRL comes up immediately, but the PTT is still blocked for the usual